Brain Anatomy

This section presents some basics of brain anatomy, including different regions that are important to psychology.

The nervous system has two main parts: (1) The central nervous system, which consists of the brain and spinal cord, and (2) the peripheral nervous system, which is made up of nerves that extend from the spinal cord to the rest of the body.

Source: Wikimedia Commons

The brain is the control center of the body and truly the most complex structure in the known universe. An adult brain consists of approximately 86 billion neurons (nerve cells) that communicate with each other across almost 500 trillion connections. Although it weighs only about 3 pounds, the brain uses about 20% of the body’s oxygen and about 25% of the body’s glucose. The brain is so important to the body that it has been carefully protected and supported. First, it is encased by the skull which, if placed on the ground, can withstand pressure of as much as 3 tons. Second, it has several thick membranes (cranial meninges), with the outermost of these membranes being a two-layered, tough fibrous membrane called dura mater, which, literally translated from Latin, means “hard mother” (our word “matter” comes from Latin materia). Third, the cerebrospinal fluid provides protection for the brain and the spinal cord while also transporting nutrients to and the waste from the central nervous system. Fourth, the brain is protected by the blood-brain barrier which limits the material that can pass from the blood to the cells of the brain and spinal cord.

Source: ThoughtCo.com

DIFFERENT AREAS OF THE BRAIN
There are many ways to discuss divisions of the brain. The terms forebrain, midbrain, and hindbrain are commonly used to denote the brain’s general geography. In adults, the midbrain is dwarfed by the other two areas, particularly the forebrain. Also, the brain is lateralized and symmetrical, which is why, as an example, we have two amygdalae, two hippocampi, two temporal lobes, etc.

Another way to think of brain division is in terms of the brain stem (automatic functions necessary for survival), the cerebellum (subconscious motor movement), and the cerebrum. Whereas the first two structures make up the hindbrain, the cerebrum and the forebrain are one and the same. 

Source: Wikimedia Commons

In psychotherapy, the most relevant area of the brain is the cerebrum. Even the limbic system, which has received a great deal of attention in recent years, resides in the subcortical region of the cerebrum/forebrain.

The Cerebrum
The cerebrum (from the Latin word for “brain”) accounts for approximately 85% of total brain mass. The cerebrum consists of right and left hemispheres, which are joined by two bundles of axons (fibers) that provide communication between the two sides of the brain.

The Cerebral Cortex
When we look at the brain, we are seeing its outer layer called the cerebral cortex, or cortex for short (cortex is Latin for “bark” or “covering”). Gray on the outside (hence, “the gray matter”) and folded, the cortex accounts for about 40% of total brain mass. The folding is what allows for an increased overall surface, which in turn accommodates more neurons and higher functions. The cerebral cortex is the most recently developed structure in the history of brain evolution.

The Lobes of the Cerebral Cortex

Source: Serious-Science.org

The cortex is divided into four lobes, with the lobes traversing the hemispheres. The lobes are named after the four skull bones that are positioned over them: frontal, temporal, parietal, and occipital.

The frontal lobe is the largest and consists of the motor cortex and the prefrontal cortex. The motor cortex controls voluntary muscle movement, including fine movements such as moving one finger at a time.

Source: Wikimedia Commons

The Prefrontal Cortex (PFC) 
The PFC is a large area that begins directly behind the eyes and the forehead and occupies the front third of the brain. Because some of the features of its neurons are larger and more numerous than in any other region of the brain, the PFC can integrate an enormous amount of information and coordinate the functions of the different parts of the brain. 

Source: Wikimedia Commons

The PFC gets a significant amount of attention in neuropsychology because it manages functions that make us distinctly human. In psychotherapy, the PFC is our ally because it is the center of our conscious thought. Whereas other parts of the brain are reactive, instinctual, and/or automatic, the PFC gives us the power to be responsive and make deliberate choices. 

PFC capacities include executive function & self-regulation, personality expression, emotional regulation, awareness of one’s own emotions, theory of mind, imagination, and the understanding and production of language (both spoken and written).

Executive function & self-regulation is a set of higher-order cognitive skills, including the following: abstraction; logic; problem-solving; mental flexibility (the ability to sustain or shift attention as necessary and to apply different rules in different settings); multitasking; goal-setting and the subsequent planning, coordination, and implementation of necessary steps; task prioritization; sustained attention and filtering of distractions; analysis and, if necessary, modification of own behavior; decision-making; cognitive flexibility; thinking through the consequences of behavior; and impulse control/behavioral inhibition. The PFC’s ability to perform such functions is often likened to an air traffic control system at a large, busy airport.

Executive function and self-regulation skills are crucial for learning and development. They enable us to behave in positive ways, make adaptive choices, develop a healthy sense of self, and build healthy interpersonal relationships.

Since the brain develops from the bottom up, the prefrontal cortex is the last area to mature in the frontal lobe and brain in general. Read below for a brief section on the phases of brain development.

The Limbic System
This set of interlinked structures is in the subcortical region of the cerebrum. It is called “limbic” because its structures form a border (limbus in Latin) around the brainstem. The structures that make up the system are particularly important for emotion, motivation, and memory storage and retrieval. The system also plays a part in the connection between conscious functions and unconscious autonomic functions. 

In popular jargon, the limbic system is often referred to as the “emotional brain” or the “feeling and reacting brain” because of its role in fear, anxiety, and the instinctual fight-flight-freeze response. The Brain & Anxiety section of Neuropsychology has a more detailed discussion about the role of the limbic system.

Source: Wikimedia Commons

THE PHASES OF BRAIN DEVELOPMENT
The brain develops from the bottom up, just the way a house is built. We are not born with higher-order cognitive skills but with the potential to develop them. Different areas of the brain begin and mature in their development at different times.

Source: Harvard University, Center on the Developing Child

There is still a great deal we do not know about the brain. In general, we know that our DNA controls how the brain establishes basic neural circuits that are present at birth. Thereafter, environmental experiences have a disproportionate impact on the brain’s development, with lifelong consequences. The brain architecture from our earliest years provides the foundation for future learning and patterns of thought, behavior, and emotion. This is discussed further in the Adverse Childhood Experiences section. 

Here are some more facts about the timeline of brain development, according to what we know so far:

  • At birth, the brain is about 25% of its adult size and has only the basic wiring patterns outside of those needed for survival. The spinal cord and the brain stem are well developed, while the cerebellum is present in rudimentary form
  • By age 2, the brain has increased to about 75% of its adult weight
  • The brain reaches its largest physical size by age 11 for girls and 14 for boys
  • Each part of the brain has a “window of opportunity” when it grows and develops the most, even though it has the ability to change throughout the person’s lifetime
  • During the first 3 years of life, the brain is in a phase of rapid proliferation when more than 1 million new neural connections form every second
  • After age 3, unused neural connections are reduced through the process called pruning, which increases the brain’s efficiency
  • The pruning continues through late adolescence, at which point the connections are reduced to about 500 trillion
  • The very last part of the brain to mature—around 22-25 years of age—is the prefrontal cortex

Sentis Brain Animation Series on YouTube is a compilation of short, highly informative animated features about the brain. Click here to access the entire series.